Resin-plated products treated by various resin plating methods have heretofore been proposed. On the other hand, the number of accidents is increasing with respect to resin-plated products available on the market. For example, accidents have occurred in the case of resin-plated products which are frequently handled directly by hand such as products used as substitutes for washing metal fittings, e.g., faucets and shower parts in bathrooms, and automobile parts, e.g., radiator grille, door opening/closing handles and interior decorative parts. In these resin-plated products there has occurred an injury accident such that a resin-plated film floats and a hand is cut by the resulting sharp portion.
For example, in the case of an automobile indoor handle formed by molding with use of PC/ABS resin, a so-called “blister” may occur from a parting portion of a resin-plated product, as shown in FIGS. 6 and 7 which are enlarged photographs of sections of resin-plated products. The blistered portion of the resin-plated product is in a floated state of a plating film as indicated by an arrow in FIG. 6. For example, when the resin-plated product is peeled with an acid, ply separation of a thin film occurs in the blister portion and at the same time the plating film assumes a floating state.
As shown in FIG. 7, the ply separation of a thin film of the resin-plated product may occur also in a resin molding which incorporates a resin apt to form a layered structure during molding such as PP resin or incorporates a different kind of incompatible resin. This was confirmed when such a thermal shock test or thermal cycle test as will be described later was performed for resin-plated products using PC/ABS (polycarbonate/ABS) resin or ABS resin. When viewed from the standpoint of molding conditions for resin moldings, the phenomenon in question tends to occur more frequently when the injection speed is high or when there evolves much gas of a low-boiling fraction. The state of occurrence of the phenomenon in question also differs depending on the product shape or the mold structure.
FIGS. 8 to 10 are photographs of a resin surface of a resin molding taken through a transmission electron microscope (TEM).
With respect to a resin molding obtained under the same conditions as those adopted for a product which underwent ply separation when there was conducted such a strong thermal shock test as illustrated, the present inventor checked a state of deformation of the resin surface with use of photographs taken through a transmission electron microscope (TEM).
FIG. 8 is a photograph showing the state of a cavity surface (a front surface) of a resin molding. In the same figure, a circular or black dot-like portion represents a rubber component contained in resin. In this resin molding, the rubber component is uniformly dispersed in a circular shape in the resin surface of the cavity surface and a molding stress in the resin surface is reduced.
FIG. 9 is a photograph showing the state of a parting portion (the center and the vicinity thereof) of the resin molding. In this state of the resin molding, as compared with the cavity surface shown in FIG. 8, the rubber component in the surface resin layer is stretched like a bamboo leaf and is in a layered form. Deformation is found also in the rubber component located in a lower portion of the section and there is a residue of a molding stress.
FIG. 10 is a photograph showing the state of a parting portion (a front end) of the resin molding. In this state, the rubber component in the resin surface layer is deformed to a greater extent than the parting portion shown in FIG. 8. Further, the proportion of the rubber component located in a lower portion of the section is smaller than that of the parting portion shown in FIG. 9 and the dispersion thereof is sparse.
Such a concentration of the molding stress on the parting portion is presumed to be a cause of thin film ply separation in the surface resin layer in a state of excess heat history of the resin molding. In the surface resin layer during a resin plating process, innumerable anchor holes are formed and hydration occurs by etching, so that deterioration is unavoidable in the surface resin layer of the resin-plated product. In the hydrated layer there may occur hydrolysis of the resin due to a synergistic action between water or a slight amount of residue of a plating chemical and an excess heat history.
Thus, the blister phenomenon of the resin-plated product is a phenomenon in which the resin surface floats together with the plating film adhered thereto not due to imperfect contact between the plating film and the resin but due to ply separation of a thin resin film caused by heat history applied to the resin-plated product. That is, the floating of the plating film in the resin-plated product is attributable to the resin molding or feed resin itself, which is unavoidable in the resin plating process.
There also is a case where a problem in the manufacturing process is an obvious cause like imperfect plating-resin contact or intermetallic separation in the case of a multi-layered plating film.
Even if a problem exists in the manufacturing process, it is often misunderstood in appearance that the cause is separation or floating of a metal plating in a resin-plated product. In many cases, the true cause is not imperfect contact between resin and metal plating film, but is peeling of a thin surface resin film of a resin molding which occurs when a resin-plated product is exposed under a specific environment involving high and low temperatures and repetition thereof.
In view of this point there have been proposed plating methods for producing resin-plated products having a good plating appearance. For example, like “Method for improving the appearance of resin-plated products and products obtained by the method” described in Japanese Patent Laid Open No. 2004-300566 (Patent Literature 1), there has been proposed a method for improving the appearance of a resin-plated product, involving incorporating a solid substance other than a main component into a synthetic resin which constitutes a synthetic resin product, for the purpose of modifying or improving the synthetic resin, and forming on the resin surface fine concaves and convexes for irregular reflection of light by electrolytic nickel plating.
Patent Literature 1:
Japanese Patent Laid Open No. 2004-300566